The third generation partnership project (3GPP) is currently working on standardization the next generation of mobile communication system denoted Long Term Evolution (LTE). The architecture of the LTE system is shown in FIG. 1. In FIG. 1 the logical interfaces (S1) between the evolved Node Bs (eNBs) and the Mobility Management Entities (MME)/Serving Gateway (S-GW) and the interfaces (X2) between the eNBs are shown.
In LTE the downlink is based on orthogonal frequency division multiplexing (OFDM) while the uplink is based on a single carrier modulation method known as discrete Fourier transform spread OFDM (DFT-S-OFDM), see 3GPP TR 36.300, Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access (E-UTRAN); Overall description; Stage 2, V8.2.0.
The coverage of a cell in a wireless network depends on numerous parameters. Some of them are related to the cell selection procedure, determining the most suitable cell for establishment of communications links. Such parameters can be seen as relative parameters, since the coverage of one cell may be expanded and other cells in the vicinity will be diminished accordingly.
Other parameters can be seen as absolute parameters, and are related to the link quality alone, essentially whether at least one cell can provide acceptable link quality for communications on a given location.
The primary means to change the coverage area of a cell is to change the reference signal power or the orientation (tilt, azimuth, height) of the serving antenna branch. Such action will change the area where the cell is perceived as the main alternative for communications, and will reduce its interference to users in areas where the cell is not perceived as the main alternative.
The antenna orientation is changed by adjusting one or several of the following.                Vertical tilt, either mechanical (the mounting angle is altered) or electrical (antenna elements internally in the antenna branch are altered, changing the antenna pattern).        Horizontal beam direction (azimuth)        Height        
Each cell in a network is identified by a globally unique identity GID, and a locally unique physical cell identity PCID. The former is a unique bit string, typically long, signalled in the system information, while the latter is an integer such as 0-503 in LTE, and 0-511 in Wideband Code Division Multiple Access (WCDMA) associated to a physical reference signal sequence which the mobile can use to identify a cell on the physical layer. When a mobile station discovers a candidate cell it reports PCID of the cell to its serving cell.
In LTE, if this PCID is unknown to the serving cell it can request the mobile to decode and report the globally unique GID of the cell to uniquely identify it. This enables neighbour cell relation lists to be established automatically by the radio base station evolved Node B (eNodeB). The neighbour cell relation list changes are also sent to the domain manager and/or some other central node, which maintains an updated logical network model, including the neighbour cell relations. The eNodeB receives network addressing information about the candidate cell and is then able to setup a direct X2 connection between the two eNodeBs.
In WCDMA, the Radio Network Controller (RNC) manages a list of candidate cells, and sends such a list to the mobile station—the monitored set. If a PCID outside this list is discovered, the mobile can report such a cell as well—the detected set cell. If the detected set cell can be identified in RNC, then it can be possible to perform handover also to such a cell. If the detected set cell can not be identified in a central node, e.g. in an Operation and Maintenance O&M node, most likely handover is not possible, but the cell can be considered for inclusion in the monitored set.
In both LTE and WCDMA, the PCIDs are not globally unique, but with careful assignments, they can be locally unique which means that the mobile can report a candidate cell by its PCID, and the serving cell can determine the likely cell if the PCID is listed in the serving cells neighbour cell relation list, and initiate handover to this cell. Also in this case, a central node can maintain a logical network model including the neighbour cell relations.
To optimize the antenna orientations, and other cell size optimizations, is an information intensive task, since the coverage needs to be carefully explored. One option is to obtain information from a cell planning tool, and rely on the path loss predictions to be accurate. Another option is to obtain the information from extensive drive tests. However, this is a work intensive task, very costly and highly inefficient for determining the need for antenna re-orientation.
Hence, there exists a need for a method and apparatus that enables more efficient cell size optimization, for example antenna re-orientation procedures.